The invention relates to a method for the manufacture of laminated grinding disks, especially laminated cut-off and rough-grinding disks for free-hand grinding, in which mixtures of grinding grits and binding agents, as well as fillers in some cases and reinforcements in some cases, are placed in a mold in layers with the interposition of at least one layer of vibration damping materials, and are pressed to form a sandwich and the sandwich is cured.
In grinding and cut-off work, but especially free-hand grinding, vibrations develop which create a considerable amount of noise, and these vibrations occur both on the workpiece and on the grinding machine and on the grinding disk itself. Although it is possible in the case of stationary machines to damp these vibrations at least partially, or to place the machine itself in an enclosure and thus reduce the noise to the benefit of the operating personnel, this possibility does not exist in the case of hand grinding work in which cut-off or roughing disks generally known as flex disks, are used. In line with the progress of environmental awareness, therefore, there is a considerable need for grinding disks which produce less noise when used. Grinding disks which, on the basis of their construction, have less tendency to produce vibrations are known as noise-damped grinding disks, and are disclosed in this form in DE-OS 26 10 580, DE-OS 26 32 652, and AT-AS 46 15/82. All these proposals have in common that, between the actual grinding layers, noise damping layers are disposed, which can consist of a polymer or a vibrationdamping film, e.g., nitrile rubber.
The methods of manufacturing these known grinding disks, however, are very complex. For example, it is stated in DE-OS 26 32 652 that two finished, so-called "grinding plates" having a certain diameter-to-thickness ratio, are bound together by a polymer layer which is at least 0.2 mm thick and has at most the thickness of the "grinding plates." The polymer, which can be an adhesive, is applied in a paste or in a liquid or molten state between the two "grinding plates" and then dried, hardened or solidified, in order thus to bind the two "grinding plates" tightly together. A thermoplastic resin can be used as the polymer, but preferably plastics which can be set by heat treatment are used.
The method is very complex, because in this method at first finished "grinding plates" have to be made in order to be joined together afterward.
DE-OS 26 10 580 also discloses a device having a plurality of thin grinding disks forming the layers of abrasive material are coated with a binding agent, placed one on the other, and compressed. To achieve greater thicknesses in the damping layers, disks of thermoplastic film and disks of abrasive material can be layered alternately one on the other and pressed together with heat so that the thermoplastic material is bonded to the disks of abrasive material.
In contrast to the two disclosures discussed above, which set out from an already finished "grinding plate," AT-AS 46 15/82 provides that a vibration-damping film of, for example, nitrile rubber is placed on a grinding grit mixture in a press and pressed together with the mass of grinding grits. The grinding disk sandwich thus produced is clamped between pack plates and hardened in the oven. Due to the fact that, in each case, a film of nitrile rubber has to be stamped out to fit the mold, or this film has to be first duplexed onto the fabric and then laid in the press together with the latter, and after it is pressed the grinding disk sandwich has to be clamped between pack plates and cured in the oven, the process is decidedly time-consuming and hence involves high labor costs.
It is furthermore disadvantageous that the sandwich always springs back up slightly after pressure, which is attributed to the elasticity of the vibration damping film. This degrades the bond to the adjacent grit layers, so that the danger exists that some areas of the grinding grit layers will not be in contact with the film layer and thus no bond will be formed.
The present invention is therefore addressed to the problem of devising a method which will assure perfect adhesion between the abrasive material and the noise-damping material over the entire area of the layer, and in which this sound-damping layer can be applied quickly and simply.